1. Field of the Invention
The present invention relates to a solvent exchange process, and in one embodiment, a process that is capable of separating an organic acid such as ascorbic acid from an alcoholic phase.
2. Background Art
Attempts to efficiently and effectively separate an organic acid from an alcoholic phase in which the acid resides have proven to be quite inefficient. In particular, one environment which these inefficiencies have been particularly apparent relates to the production of ascorbic acid.
L-ascorbic acid (vitamin C) has been produced commercially by way of chemical fermentation processes starting from glucose or sorbose. A common intermediate generated during the fermation process is 2-keto-L-gulonic acid or its protected form of diacetone-2-keto-L-gulonic acid. In the case of 2-keto-L-gulonic acid, a process involves esterification of the sugar with methanol followed by cyclization using stoichiometric amounts of base. This process has evolved from the original Reichstein process (T. Reichstein, A. Grussner, Helv. Chim. Acta 17, p. 311, 1934).
Recent modifications to the Reichstein process have become more prevalent as alternative fermentation processes for producing 2-keto-L-gulonic acid directly from glucose or sorbose have been reported. These processes have eliminated or removed some of the chemical processing steps prior to production of 2-keto-L-gulonic acid in the Reichstein process. However, these processes have necessitated the separation and purification of ascorbic acid from its alcoholic or aqueous alcoholic solution, all initiated from an alkali metal ascorbate.
The esterification and cyclization processes employed in the art utilized an organic solvent with the cyclization step and therefore eventually include an isolation of either solid alkali ascorbate or solid ascorbic acid by dissolving the solid in water with subsequent crystallization from water. A typical arrangement is illustrated by FIG. 1 in which the feed involves ascorbic acid in an alcoholic phase. The solids are removed by a series of crystallization steps and then dissolved in, and recrystallized from, water to provide the desired final product.
As can be seen, this series of processing steps necessitates a complex separation system. Solid-liquid handling equipment such as crystallizers are needed for switching from the organic solvent to an aqueous-based solvent system as well as similar solid-liquid handling equipment as required from isolating purified ascorbic acid from water. Such complexities greatly add to the cost of the overall process.
Thus, the need still exist for a method of more efficiently removing acids, and in particular, ascorbic acid, from alcoholic phases thereby both simplifying and making more cost effective overall purification and recovery process.